What is the meaning of Wager_of_battle?

The giving of gage, or pledge, for trying a cause by single combat, formerly allowed in military, criminal, and civil causes, and finally abolished in 1819. In writs of right, where the trial was by champions, the tenant produced his champion, who, by throwing down his glove as a gage, thus "waged", or stipulated, battle with the champion of the demandant, who, by taking up the glove, accepted the challenge.

Source: wiktionary.org